1. Field of the Invention
This invention relates to annunciator circuits, and more particularly to a low battery voltage annunciator circuit which reduces the amplitude of the annunciator output signal in order to reduce the power consumption of the annunciator circuit which in turn results in an extension of the time period a low battery alert can be generated.
2. Description of the Prior Art
In the past, especially in paging environments, there has been a need to provide an audible low battery voltage alert to indicate to the user that the battery powering the radio paging device either needs to be recharged or replaced. Such prior art circuits have been designed such that when the battery voltage level has dropped to a predetermined level, the transducer driver amplifier is activated and drives the transducer at a relatively constant amplitude until the user acknowledges the alert by turning off the radio paging device and replacing or recharging the battery.
However, in many instances the user of a paging device is not wearing the radio paging device at the time the battery source is depleted to the predetermined voltage level at which the alert signal is activated. Thus, if the low voltage alert is sounded while the user is away from the radio paging device, the battery source may be rapidly depleted to a level whereby the alert is no longer sounded. Upon return to the location of the paging device, the user would then be unaware that the radio paging device has been rendered inoperative by way of the depleted battery and an important message may be missed.
One such prior art device includes a voltage comparator having its inputs connected to the battery supply voltage and a voltage reference source, respectively. When the battery voltage drops to the level of the reference voltage, the comparator is triggered and generates an output signal. The output signal from the voltage comparator is directed to a microprocessor which, upon sensing the comparator output signal generates a squarewave output signal. The squarewave signal is directed to a transducer driver. The transducer driver is turned on by the squarewave signal and generates an output signal to drive a transducer which generates an audible alert. The audible alert is generated until the pager is turned-off manually or until the battery is depleted to such a low level it cannot supply enough power to drive the transducer.